In wireless communication, it is generally desired that the limited frequency resources be used effectively. In order to effectively utilize the frequency resources, the radio waves of the same frequency are used repeatedly as close in distance as possible, for example. In that case, the communication quality degrades due to the co-channel interference from the neighboring base station apparatuses or the like that use the same frequency. One of the techniques to prevent the degradation of communication quality due to the co-channel interference is adaptive array antenna technology. In the adaptive array antenna technology, the signals received by a plurality of antennas, respectively, are weighted with different weighting factors and then combined together. For example, the weighting factors are adaptively updated in such a manner as to reduce the error between a signal to be referred to and the combined signal.
To adaptively update the weighting factors, adaptive algorithms, such as RLS (Recursive Least Squares) algorithm and LMS (Least Mean Squares) algorithm, are used. There are also cases where the weighting factors are calculated based on the response factors in a channel between a transmitting side to a receiving side. There are also cases where a radio apparatus equipped with an adaptive array antenna technology derives transmitting weight factors based on the weighting factors and response factors derived from the received signals and then the signals to be transmitted are transmitted after having weighted with said transmitting weighting factors. In this manner, in the adaptive array antenna technology the desired components are extracted from the received and the directivity at the time of transmitting the signals is adjusted, so that the degradation of the communication quality due to the co-channel interference can be prevented (See Patent Document 1, for instance).    [Patent Document 1] International Publication WO00/079702 Pamphlet.
The multiple access technique utilizing the adaptive array antenna technique is space division multiple access (SDMA) or path division multiple access (PDMA). In a base station apparatus using SDMA, a time slot in the same frequency is spatially divided in plurality, based on the adaptive array antenna technique, for example, and the radio channels associated respectively with the divided spaces are allotted to terminal apparatuses. In this manner, said base station apparatus transmits data to the terminal apparatuses to which the radio channels have been allotted.
Under these circumstances, the inventors of the present invention came to recognize the following problems to be solved. In a case where the intensity difference of signals received respectively from a plurality of terminal apparatuses multiplexed by SDMA is large or in a case where spatial correlation values of a plurality of terminal apparatuses multiplexed by SDMA are large, there are cases where the base station apparatus cannot achieve sufficient spatial separation of a plurality of terminal apparatuses. For the former case, this is because a plurality of signals, having difference greater than the difference between the maximum signal intensity and the minimum signal intensity, in the antenna directivity realized by the receiving weight vectors exceed a separation limit achievable by the adaptive array. Also, in a case where difference in power among a plurality of terminal apparatuses is large, the signal of a user in the side of small power may be hidden behind those in the side of larger power or enough dynamic range cannot be obtained, so that the user signals will not be estimated accurately.
For the latter case, this is because the arrival angles of signals transmitted from a plurality of terminal apparatuses are close to one other. Even in a case when the signals received from a plurality of apparatuses are separated according to the directions, there are cases where no correspondence is established between the respective signals thus separated and a plurality of terminals. That is, it is difficult to establish correspondence between the terminal apparatuses and the arrival directions of signals or the receiving weight vectors. Further, since the transmission processing is carried out based on the above receiving processing, the incompleteness of spatial separation in a plurality of terminals at the time of receiving will affect the transmission performance.